1. Holding time for most intermediate storage vessels, half full, is 10 minutes. 2. Holding time for feed tank to a furnace, half full, is 30 minutes. 3. Optimum L/D ratio is 3, however a range of 2 to 5 is common. 4. Vessels of less than 4 m3 is vertical mounted on legs or brackets. 5. Vessels between 4 m3 and 40 m3 is horizontal with saddle support. 6.